Effect of Mechanical Loading on Electrical Conductivity in Porcine TMJ Discs

Abstract

The objective of this study was to examine the impact of mechanical loading on solute transport in porcine temporomandibular joint (TMJ) discs using the electrical conductivity method. The electrical conductivity, as well as ion diffusivity, of TMJ discs was determined under confined compression with 3 strains in 5 disc regions. The average electrical conductivity over the 5 regions (mean ± SD) at 0% strain was 3.10 ± 0.68 mS/cm, decreased to 2.76 ± 0.58 mS/cm (-11.0%) at 10% strain, and 2.38 ± 0.55 mS/cm (-22.2%) at 20% compressive strain. Correspondingly, the average relative ion diffusivity (mean ± SD) at 0% strain was 0.273 ± 0.055, decreased to 0.253 ± 0.048 (-7.3%) at 10% strain, and 0.231 ± 0.048 (-15.4%) at 20% compressive strain. These results indicated that compressive strain impeded solute transport in the TMJ disc. Furthermore, our results showed that the transport properties of TMJ discs were regiondependent. The electrical conductivity and ion diffusivity in the anterior region were significantly higher than in the posterior region. This regional difference is likely due to the significant differences of tissue hydration between these 2 regions. This study provides important insight into the electrical and solute transport behaviors in TMJ discs under mechanical loading and aids in the understanding of TMJ pathophysiology related to tissue nutrition.

Electrical conductivity and ion diffusion in porcine meniscus: effects of strain, anisotropy, and tissue region

“…This is likely because meniscus composition is most like that of TMJ tissue, which also has a relatively low GAG content as compared to articular cartilage or intervertebral disc (Almarza and Athanasiou, 2004). The strain-dependent behavior of electrical conductivity and relative ion diffusivity found here is similar to results in the literature for other cartilaginous tissues (i.e., meniscus, articular cartilage, intervertebral disc, TMJ), which showed that static compression leads to reduced solute diffusivity and/or electrical conductivity Jackson et al, 2008;Kleinhans et al, 2015;Kuo et al, 2011;Quinn et al, 2000;Quinn et al, 2001;Wright et al, 2013;Yuan et al, 2009). This change is likely due to reduced tissue water content caused by fluid exudation during compression.…”

“…Due to the low GAG content ( $ 2-3% dry weight) in meniscus compared to other cartilaginous tissues, it was considered an uncharged tissue. The relative diffusivity (D=Do) of NaCl can be related to the conductivity measurements by (Gu et al, 2004;Kuo et al, 2011;Wright et al, 2013):…”

“…This value is the averaged relative diffusivity of Na þ and Cl À ions, which were assumed to carry the current as the primary ions in PBS solution (Kuo et al, 2011;Wright et al, 2013).…”

“…The electrical conductivity of several cartilaginous tissues has been investigated, see Table 1. These studies have found that conductivity is directly correlated to tissue water content Gu et al, 2004;Jackson et al, 2009;Kuo et al, 2011;Wright et al, 2013), and is strain-dependent Kuo et al, 2011;Wright et al, 2013). Better understanding of electromechanical properties of tissues, including conductivity and ion transport, and their relationship to tissue composition and relevant loading conditions, can provide essential information about endogenous electrical signals, which play a key role in directing resident cellular activity.…”

“…Electrical conductivity can be used to estimate the relative ion diffusivity in a tissue (Gu et al, 2004;Jackson et al, 2006;Kuo et al, 2011;Wright et al, 2013). Elucidating transport properties in meniscus is important given that much of the adult meniscus is Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com avascular (Makris et al, 2011).…”